If a short-circuit trouble occurs in the branching circuit of power distribution system, in order to avoid the power failure of entire power distribution system, it is important to quickly cut off the circuit breaker inserted to such branching circuit and thereby to keep the condition of the circuit breaker in the main circuit closed for a short period of time against a short-circuit. However, in this case, it is required that the contactor structure of the circuit breaker have sufficient capacity so that the temperature rise is controlled. FIG. 6 shows an example of circuit breaker of the prior art and FIG. 7 shows a structure of the movable contactor thereof. In the figures, the one end of movable contactor piece holder 1 is supported by an axis pin 3 to a case accommodating such circuit breaker and the holder is swayed through a toggle device 5 by moving handle 4 to the right or left. 6 is an operation spring attached to the handle 4. The movable contactor piece 7 is mounted to a coupling pin 8 between the side walls of holder 1 and the main movable contact 9 is fixed to the one end. When the holder 1 sways, such main contact is in contact with or separated from the fixed contact of the fixed contactor 10 to be connected to the side of power supply. A connecting conductor 11 which is flexible in its thickness direction and is composed of laminated thin copper plates is connected to the other end of movable contactor piece 7 and is then connected to a load through an over current detecting circuit not shown. The movable contactor piece 7 is divided into two segments as shown in FIG. 7 in order to ensure the contact of main movable contact 9. Therefore, the connecting conductor 11 is provided with the slit 11a in the side to be connected to two movable contactor pieces 7. 12 is an arc movable contactor fitted between two movable contactor pieces 7 and a contact spring 13 is respectively attached respectively between the movable contactor piece 7 or arc movable contactor piece 12 and holder 1. A lever 14 is engaged with the latch 15 in the side of over current detector as shown in FIG. 6. But when an over current flows, the latch 15 is disengaged, the toggle device 5 crumbles and thereby the movable contactor piece 7 separates from the fixed contactor 10.
This circuit breaker ensures easy sway of movable contactor, endures many times of opening and closing operations and allows a heavy current to flow. The connecting conductor connected to the movable contactor piece is formed by stacking many thin copper plates and is flexible in the thickness direction. Moreoever, such movable contactor piece is long (L) and thereby total length of circuit breaker becomes long. When many movable contactor pieces are supported between holders in order to ensure a high current capacity, the main movable contact and the fixed contact are respectively in contact individually. Therefore, such method is effective for suppressing temperature rise of contact and reducing an electromagnetic repulsion force. But, it also results in the disadvantage that it is required to provide many slits to the connecting conductor and thereby the circuit breaker becomes expensive.
Thus, the structure of contactor as shown in FIG. 8 has also been proposed. The movable contactor piece 7 is provided by a coupling pin 8 and axis pin 3 between the side walls of holder 1 which is swayed by a handle 4 through a toggle device 5 as in the case of that shown in FIG. 6 and it sways together with the holder 1. Thereby, it is in contact or separated form the contact of fixed contactor 10. This movable contactor piece 7 is provided with protruded area 7a like an arc at the other end of the same surface as the main movable contact 9 fixed at the one end thereof and is slidable in contact with at recess 11b like an arc provided to the connecting conductor 11. Accordingly, a simple structure is possible for the connecting conductor. However, since the movable contactor piece is movable supported with an axis pin 3 by an elongated axis hole, when a current I flows to the connecting conductor 11 from the movable contact piece 7 as indicated by an arrow mark of solid line, an electromagnetic repulsion force F--F as indicated by an arrow mark of dotted line is generated between the protrusion 7a and recess 11b, resulting in poor contact. Therefore a compression spring 16 is used for obtaining sufficient contact between them. But since a repulsion force F--F between them is proportional to a square value of current I, when a heavy current such as a short-circuit flows, the repulsion force F--F becomes very large and a compression force of spring 16 must usually be intensified. As a result, a large friction force is generated at the time of usual opening or closing. This is a disadvantage for the opening and closing operations.
It is an object of the present invention to provide a contactor structure of a small size for use in an economical circuit breaker which eliminate the discussed disadvantages of the prior art and has a large single-time current rating.
To this end, the invention is a contactor structure from a circuit breaker which includes a first conductive connecting member which remains fixed and a second conductive member which sways with respect to the fixed member whereby the main contact on the second member makes or breaks connection with a fixed contact. The first member has one end bifurcated to form a pair of legs each of whose free end has an arc-like inner surface in cross section and the two arc-like surfaces define between them a substantially circular receptor space. The second member has the movable main contact at one end and at the other end a contact region which is substantially circular in cross section and this end is enclosed within the receptor space and makes sliding contact with the arc-like surfaces as the second member is swayed with respect to the first member. The second member is rigidly coupled to the holder which can be toggled to make or break the contact.